The study provides some clues as to why the political climate in the United States appears to be increasingly polarized. It suggests this polarization could be related to a desirability bias rather than a confirmation bias.

“Given the well-known polarization and disagreement that exist over certain issues in the realm of politics, we were interested in what factors cause people to revise their beliefs in the political domain,” explained the study’s corresponding author, Ben Tappin of Royal Holloway, University of London. “On the one hand, classic findings from the late 1970’s suggest that we update our beliefs to incorporate new information that confirms (vs. disconfirms) our prior beliefs — even if we receive a balanced stream of both confirming and disconfirming information. This bias towards confirming information in belief revision has been suggested to underpin belief polarization.”

“On the other hand, more recent findings from the literature on self-belief revision (that is, research looking at how people revise their beliefs about themselves) suggest a similar but slightly different mechanism,” he told PsyPost. “Specifically, that we revise our beliefs to incorporate new information that is desirable (vs. undesirable). In past research, these two biases (“confirmation bias” and “desirability bias”) have been conflated. The aim of our study was try and tease these two biases apart to get a clearer picture of what may be driving belief revision in the political domain.”

The researchers examined supporters of Donald Trump and Hillary Clinton, and found that both groups assigned greater weight to information that was consistent with their desires. Trump supporters assigned more weight to a fictional poll suggesting that Trump would win the upcoming 2016 election, while Clinton supporters assigned more weight to a fictional poll suggesting that Clinton would win.

But there was little evidence of a confirmation bias. Most Trump supporters who believed Clinton was going to win did not assign more weight to polls confirming that belief, and the same was true of Clinton supporters who believed Trump would win.

In other words, people were the most likely to change their beliefs if the new information lined up with the election outcome they wanted.

“The mechanisms by which people revise their beliefs about political matters are nuanced and complex,” Tappin told PsyPost. “Our study provides evidence for this complexity: specifically, by showing that biases related to our prior beliefs and our desires are dissociable, and this may have implications for political belief revision.”

The study was based on 811 U.S. adults who completed an online survey in September 2016.

“We did not investigate biased search for new information, or biased evaluation of new information, but only bias in belief revision,” Tappin said. “The former two surely underpin a lot of belief polarization that we see in society; our study is, of course, just one piece of a much larger jigsaw. It remains an open question, for example, whether confirmation and desirability biases are similarly dissociable when we search for, and/or evaluate new information.”